You ask great questions with no easy answer. Angular 2 is a huge improvement so I’d lean heavily toward using it over Angular 1 at this point. Since it’s in Beta, you should be relatively safe from any big shifts before the final 2.0 release. However, I wouldn’t actually push the app to prod until Angular 2.0 goes out of beta, so whether that is practical depends on your timelines (and your best guess on when Angular 2 will come out of beta).
Regarding your complexity question, both Angular 2 and React with Flux/Redux can scale to very complex apps. But the simpler the app is, the more preferable React becomes since the resulting app is likely to weigh less. And the more complex it becomes, the more libraries you’ll have to pull off the shelf to augment React (Flux/Redux, React Router, and so on). In those cases, Angular may become more preferable.